The Breeding Biology of the Great White Pelican Pelecanus Onocrotalus Roseus at Lake Shala, Ethiopia

Abstract

Summary. Pelecanus onocrotalus roseus is known to breed more or less regularly in Africa at Lake Shala, Ethiopia; Lake Rukwa, Tanzania; St. Lucia Bay, Natal; Abou Tougour, Chad; Kapsikis, Northern Cameroons; and Wase Rock, Nigeria; and has been observed or reported breeding at Mweru Marsh, Zambia; Lake Ngami, Botswana; Seal and Dyers Islands, South Africa; and Lake Natron, Tanzania. The Shala colony, after Lake Rukwa's, is the largest known breeding colony in Africa and is probably of crucial importance to the species in Africa. For successful breeding regular colonies of P. onocrotalus must have an assured supply offish and an inaccessible breeding site. These conditions are met at the Lake Shala colony. Assuming that a Great White Pelican consumes about 10% of body weight or about 900‐1,200 g per day, the Lake Shala breeding colony with 7,500‐12,000 pairs would consume about 3,140‐5,040 tonnes in the breeding seasons. The partially unsuccessful breeding of perhaps 10,000 pairs at Lake Natron in 1962 is described. Failure was attributed to sudden failure of the food supply. Breeding of the Great White Pelican on Lake Shala takes place throughout the year although there is a peak of numbers breeding from December to the end of March, which is in the dry season. Observations recorded in this paper cover two full breeding seasons, 1965‐6 and 1966‐7. Although during the peak period of breeding the flock at Shala is made up of 2,500‐5,000 pairs, this mass is composed of smaller units, each made up of 300‐1,200 pairs, laying more or less together with little overlap from one group to the next. Three changes occur in the plumage of the Great White Pelican towards the onset of the breeding season: (a) the development of a knob or swelling on the forehead at the base of the beak with associated expanses of brightly‐coloured bare skin, pinkish yellow in males and bright orange in females; (b) the development of a crest; and (c) the development of a yellowish band across the chest or larger areas of darker brown in the plumage. Four distinct colour‐types of breeding plumage were observed: the dark‐brown type, the brown‐breasted type, the yellow‐banded type, and the type with scarcely any suggestion of a breast patch. No correlation was found between plumage type and sex, size, length of bill or any other obvious physical feature. Group display and individual displays of the adults are described. There appears to be no special pre‐copulation display. Elaborate nests are not prepared; the male collects the nesting material, and both sexes build the nest. Nests are small, 35–60 cm in diameter (averaging 46‐4 cm), and close together (364 nests averaged 1–55/m2). Average clutch‐size is 1–88. Incubation begins with the first egg; both sexes incubate; the incubation period is probably about 38 days. The fledging period is 65–70 days, of which about the first 28–30 days are spent in the nesting area. After that the young form into groups or “pods”. The development of the young is described. When it is very small it is fed by eith...

Energy requirements of a Great white pelican (Pelecanus onocrotalus) population and its impact on fish stocks

“…Adult masses were taken to be 11.5 kg for males and 7.6 kg for females (Din & Eltringham, 1977). Mean egg mass is 177g (derived from Brown 8c Urban, 1969,assuming initial egg density of 1 .04g/cm3).…”

“…For this reason, there have been several detailed studies of its biology (e.g. Brown & Urban, 1969;Din & Eltringham, 1974;Din, 1979;Whitfield & Blaber, 1979), and attempts have been made to assess the food consumption by Great white pelican populations (Din & Eltringham, 1974;Din, 1979;Berruti, 1983), often assuming that pelicans consume daily a mass of fish equal to 10% of their body mass.…”

An ethogram of Spot-billed Pelican (Pelecanus philippensis)

“…However, the Spotbilled Pelican differs from other species of pelicans in certain behavioral aspects. Brown and Urban (1969) reported group displays in White or �reat White Pelicans (Pelecanus onocrotalus), while Schaller (1964) reported strut wal�ing in the American White Pelican. However, no such displays were observed in the SBP during courtship.…”

Parent–offspring conflict in avian families

“…Schaller 1964;Brown and Urban 1969;Din and Eltringham 1974). Chicks can also challenge parental decisions over the division of resources within the brood by monopolising access to parents, for example by barging weaker offspring to the side or by forming a dominance hierarchy through intimidation (see below).…”